Syringe plunger seal



April 22, 1947 w. H N 2,419,401

SYRINGE PLUNGER SEAL Filed Feb. 25, 1946 l a Fig. I

F'l'g. 2 .F'ig.3

Dr. William E. Hinds INVENTOR ATTORNEY Patented Apr. 22, 1947 UNITEDSTATES PATENT OFFICE.

SYBINGE PLUNGER SEAL William E. Hinds, Hillsboro, Oreg.

Application February 25, 1946, Serial No. 650,107

4 Claims.

The present invention relates to improved syringes and particularly to aplunger seal attachment adapted for use with commercially availableinjection syringes.

The most commonly used hypodermic injection syringe comprises a glassbarrel and a glass plunger, the inner cylindrical surface of the barreland the outer cylindrical surface of the plunger of each syringe beingground and mated with high degree of accuracy to assure a close fitbetween the barrel and plunger. Glass is a preferred material for themanufacture of syringes since it is easily formed, readily sterilizedand permits inspection of the contents of the syringe so that theoperator can be certain that the injection is not contaminated by anyforeign matter, air bubbles and the like which would interfere with theoperation of the syringe or be injurious to the patient. However, evenwhen the barrel and plunger are ground to obtain the closest slidingfit, more or less leakage of the contents of the syringe takes placebetween these two parts as the plunger is pushed in. This isparticularly true when the injections are made at a slow rate. Forexample when the rate is of the order of 1 to 2 cc. per hour for a 20cc. syringe, the liquid may seep past the plunger at such a rate thatnone of the liquid is actually injected into the patient.

Another disadvantage of glass syringes is that the glass parts thereofare easily broken. Since the plunger and barrel of each syringe arematched during grinding thereof by the manufacturer, the plungers of twodifierent syringes of the same type cannot be satisfactorilyinterchanged to obtain a leak-proof fit, so that when either the barrelor plunger is broken, both must be discarded.

A primary object of the present invention is to provide a simple,inexpensive attachment for such syringes, which attachment willeffectively prevent leakage of the injection past the plungerirrespective of the rate at which the injection is being administered.

Another object of the invention is to provide a plunger seal for asyringe so constructed that it can be securely attached to the plungerand easily removed therefrom to facilitate sterilization of theattachment and the various parts of the syringe.

A further object of the invention is to provide an attachment forexisting syringes which will permit a greater clearance between theplunger and barrel thereof and the interchanging of plungers of varyingdiameters.

These and further objects of the invention will become apparent from thefollowing descrip-- tion when taken in connection with the accompanyingdrawing in which:

Fig. 1 is a view, partially in section, of a standard glass hypodermicsyringe provided with the attachment of the present invention; Fig. 2 isan enlarged cross-sectional view of the attachment; and Fig. 3illustrates a modified form of the attachment.

Referring to Fig. 1 of the drawing, I is the glass barrel of a standardhypodermic syringe having at one end thereof a nipple 2 adapted forconnection of a hypodermic needle (not shown). The other end of thebarrel is open to receive a cylindrical glass plunger 3 having a knob orhandle 4 at one end, the inner end 5 of the Plunger being formedsubstantially flat and at right angles to the longitudinal axis of theplunger. The inner cylindrical surface of the barrel and that portionouter cylindrical surface of the plunger which comes in contact with thebarrel during use of the syringe are ground to obtain a close, slidablefit between the two parts, the manufacturing cost of the syringesvarying directly with the degree of accuracy with which the barrel andplunger are ground and mated.

The above mentioned elements comprise the principal parts of a standardglass syringe. Such syringes are particularly acceptable to the medicalprofession because their simple design, involving no crevices, joints orthreaded connections, makes them easy to use and greatly facilitates thecleaning and sterilization thereof.

It will be noted that the closer the lit between the ground surfaces ofthe barrel and plunger, the less likelihood there is of substantialleakage of the contents of the syringe between these surfaces. On theother hand a close fit also means greater friction between these twoelements and greater possibility of breakage during assembly and use ofthe syringe. Hence for practical purposes, there is a limit on thecloseness with which the two elements can be fitted since they must beso constructed as to permit repeated disassembly for cleaning andsterilization purposes.

Depending on the degree of accuracy with Which the plunger and barrelare mated, more or less leakage takes place therebetween when theplunger is pushed in during injection of a medicant, particularly whenthe rate of injection is low. In accordance with the present invention Ihave provided an attachment. for existing syringes which is designed toeliminate completely the difficulty of leakage between the plunger andbarrel of such devices. The attachment 6 which is designed to be readilyattached to and detached from the forward end of the plunger is shown ingreater detail in the enlarged cross-sectional view of Fig. 2 ascomprising a disc I having a suction cup 8 integrally formed with oneside of the disc. The disc and cup are made of a non-toxic elastomericmaterial such as rubber, neoprene, or the like, natural rubber beingpreferred for most applications. The circumference of the disc isslightly larger than the internal diameter of the barrel 1 so thata'close fit is obtained therebetween. The suction cup 8 detachably holdsthe attachment tightly onto the end of the plunger 3. On removal of theplunger from the barrel, the attachment 6 can be readily slippedlaterally from the end of the plunger.

It will be apparent that I have provided a leakproof seal for use instandard syringes which is of simple construction and easy to clean andsterilize in that it contains no crevices, cavities or other surfaceirregularities, It is readily attachable and detachable from the end ofthe syringe plunger and can be cleaned and sterilized along with theremaining parts of the syringe,

I am aware that various syringes have previously been proposed havingrubber plungers or plunger tips to prevent leakage of the injectionbetween the plunger and the barrel. However, in these prior devices therubber member was either not attached or attachable to the plungermember as in. those cases where the rubber member forms part or all ofthe closure plug for an ampoule adapted to be inserted into a syringe orthe rubber members were permanently or semipermanently attached to theplungers so that they were difficult to clean and sterilize and whenonce removed from the plunger member for such purposes were even moredifficult to replace. The attachment of the present invention differsmarkedly from the prior art devices in the ease with which it can beattached to the plunger. For example, after the syringe has beendisassembled and the various parts thereof sterilized the whole can bereassembled without touching any parts of the syringe which come incontact with the medicant. This can be done by picking up the plunger bymeans of the knob 5, using the forward end of the plunger to expose thesuction cup portion of the seal and touching the flattened forward endof the plunger to the suction cup with a pressure sufficient merely toobtain some adhesion between these two parts; At this point the disc Eneed not be centered with respect to the longitudinal aXis of theplunger. The disc portion of the attachment is then inserted into thebarrel i. If necessary the attachment can then be centered withreference to the plunger by suitably moving the plunger into line withrespect to the barrel after which both the plunger and attachment can beinserted intothe barrel.

The modification shown in Fig. 3 is adapted to provide a more positivewiping action of the edge of the disc portion of the attachment with thesides of the barrel. In this modification, the disc portion comprises amain front portion l I of a size adapted to provide a close fit with thesyringe barrel and a backing portion i2 of a diameter somewhat less thanthe diameter of mainportion I i but sufiiciently large to-reinforce themain portion without contacting the inner surfaces of'the syringebarrel. Suction cup I 3 is integrally formed on the backing portion ofthe disc, neck- 4 [4 being as large as possible without interfering withthe suction action of cup l3.

As has been previously indicated my seal can be employed not only forleak-proofing the standard glass syringes but also for reclaimingunbroken parts of such syringes.

In any given type and'make of syringe it has been found that there isonly a very small variation in the diameters of the barrels, Althoughthese variations are sufiicient to cause substantial leakageparticularly when the smallest plunger of a given line of syringes isinserted into one of the larger barrels, the differences in diameter arenot so great that an attachment of the type herein disclosed having adisc diameter slightly larger than the smallest barrel opening cannotsatisfactorily be employed with any syringe of the same type and make.Thu by means of my attachment, an unmated barrel and plunger can bereclaimed provided the plunger can be slidably inserted into the barrel.

The attachments of the present invention are particularly adapted foruse with syringes having a barrel diameter of about one inch or less.With such attachments the thickness of the disc portion will ordinarilybe from one-fourth to oneseventh the diameter of the disc while the neck9 connecting the vacuum cup to the disc should have a diameter at leastequal to one-half that of the disc and preferably should be as large aspossible. As is also shown in Fig. 2 of the drawing the vacuum cupshould have a diameter of at least about three-fourths that of the discand ispreferably made as shallow and flexible as possible since only aminimum amount of suction is necessary to assure satisfactory adherenceof the attachment to the plunger head.

While the invention has been described with reference to the use of theseal in combination with glass syringes, it is not restricted theretosince the sealing attachment can also be employed for leak-proofingmetal or combination metal and glass syringes comprising a plungerhaving a fiat forward end to which the attachment can be secured bymeans of the suction cup.

Having decribed the invention in what are considered to be preferredembodiments thereof it is desired that it be understood that thespecific details shown are merely illustrative and that the inventionmay be carried out by other means.

What I claim is:

l. A plunger attachment for preventing leakage between the plunger andbarrel of a syringe, said attachment comprising a resilient discshapedmember and a suction cup integrally formed therewith and adapted forholding said attachment on the forward end of the plunger.

2. A syringe plunger seal adapted to be detachably held on the forwardend of a syringe plunger, said seal comprising a resilient discshapedmember having integrally united therewith a resilient suction. cupadapted to hold said seal in operating position on the end of saidplunger.

3. A rubber attachment adapted to prevent leakage between the ground,slidably engagingv surf-aces ofthe plunger and barrel of a glasssyringe,said attachment comprising arubber disc having a diameter slightl largerthan the inter-- nal diameter of the syringe barrel and a shallowsuction cup integrally formed with one .side of said disc and connectedthereto'over at least onehalf the diameter of the disc, saiddischaving athickness from about one-fourth to one-seventh: the diameter thereof,the said suctioncuphaving,

a diameter about three-fourths the diameter of with the innercylindrical surface of said barrel, and a resilient seal detachablymounted on the forward end of said plunger, said seal comprising a dischaving a diameter slightly larger than the internal diameter of thebarrel and a suction cup integrally formed with said disc for.detachably securing said seal to said plunger.

WILLIAM E. HINDS.

